src/ieee754/fpcommon/roundz.py

   1 # IEEE Floating Point Adder (Single Precision)
   2 # Copyright (C) Jonathan P Dawson 2013
   3 # 2013-12-12
   4
   5 from nmigen import Module, Signal, Mux
   6
   7 from nmutil.pipemodbase import PipeModBase
   8 from ieee754.fpcommon.fpbase import FPFormat, FPNumBaseRecord, FPRoundingMode
   9 from ieee754.fpcommon.getop import FPPipeContext
  10 from ieee754.fpcommon.postnormalise import FPNorm1Data
  11
  12
  13 class FPRoundData:
  14
  15     def __init__(self, pspec):
  16         width = pspec.width
  17         self.z = FPNumBaseRecord(m_extra=False, name="z",
  18                                  fpformat=FPFormat.from_pspec(pspec))
  19         self.ctx = FPPipeContext(pspec)
  20         self.muxid = self.ctx.muxid
  21         # pipeline bypass [data comes from specialcases]
  22         self.out_do_z = Signal(reset_less=True)
  23         self.oz = Signal(width, reset_less=True)
  24
  25         self.rm = Signal(FPRoundingMode, reset=FPRoundingMode.DEFAULT)
  26         """rounding mode"""
  27
  28     def eq(self, i):
  29         ret = [self.z.eq(i.z), self.out_do_z.eq(i.out_do_z), self.oz.eq(i.oz),
  30                self.ctx.eq(i.ctx), self.rm.eq(i.rm)]
  31         return ret
  32
  33
  34 class FPRoundMod(PipeModBase):
  35
  36     def __init__(self, pspec):
  37         super().__init__(pspec, "roundz")
  38
  39     def ispec(self):
  40         return FPNorm1Data(self.pspec)
  41
  42     def ospec(self):
  43         return FPRoundData(self.pspec)
  44
  45     def elaborate(self, platform):
  46         m = Module()
  47         comb = m.d.comb
  48
  49         comb += self.o.eq(self.i)  # copies muxid, z, out_do_z
  50         im = self.i.z.m
  51         ie = self.i.z.e
  52         msb1s = Signal(reset_less=True)
  53         comb += msb1s.eq(self.i.z.m.all())  # all 1s
  54         comb += self.o.z.m.eq(Mux(self.i.roundz, im+1, im))  # mantissa up
  55         comb += self.o.z.e.eq(Mux(msb1s & self.i.roundz, ie + 1, ie)) # exp up
  56
  57         return m